After your last comment, I thought maybe I changed the code and it's causing it to break. So, I went back and downloaded the completed project and started over. When I looked at the code behind "MainNav", I noticed it's the same code I had before, and it does not match your code. Again, I'm not sure if I'm doing something wrong or if the project is possibly wrong. Have you tried to download the project and make sure you can load and compile?